The differentiation of murine erythroleukemia cells will be studied at the molecular and cellular levels. The following areas of study are proposed: 1) Synchronization of differentiating cells to determine the relationship between the cell cyle, commitment to differentiation and the synthesis of globin mRNA. 2) Analysis of globin mRNA metabolism during the differentiation program. 3) Isolation and characterization of clones with altered capacity for differentiation. Synchronization will be carried out by unit gravity sedimentation, a technique which permits the isolation of populations of cells in all portions of the cell cycle without prior treatment with toxic agents. The focus of these studies will be to further characterize preliminary observations which indicate that a lengthening of the GI portion of the cell cycle precedes commitment to the differentiation program. Analysis of globin mRNA metabolism will be carried out following the isolation of the globin structural genes with surrounding non-coding regions of the mouse genome by recombinant DNA technology. The analysis of variant clones with altered differentiation potential will involve characterization of these clones with respect to the parameters described in our model. An analysis designed to elucidate the genetic basis for non-differentiating variants will be performed.